1. Field of the Invention
This invention relates to an image sensing apparatus which is provided with an image sensor for converting an image of an object into an electrical signal and is capable of obtaining highly accurate photometric information.
2. Description of the Prior Art
The conventional video cameras include a kind using a solid-state image sensor such as a CCD or the like. The solid-state image sensor is usable not only for the image purpose but also for a photometric purpose. With such a solid-state element used for the latter purpose, however, it takes an excessively long period of time in obtaining an apposite aperture value by driving a stop member or iris in the event of an excessive degree of deviation of the aperture position of the stop member from the apposite aperture value.
To solve this problem, Japanese Patent Application No. SHO 57-214408 disclosed a system wherein a solid-state image sensor is employed for the photometric purpose in combination with a silicon photo-cell (hereinafter referred to as SPC) which has a broader photometric range than the solid-state image sensor and the degree of exposure is controlled by the combination of the two elements. According to the arrangement disclosed by the above-cited patent application, a stop member is roughly adjusted beforehand to an apposite aperture position (or a tentative aperture value) on the basis of a light quantity value measured by means of an SPC or the like prior to the normal operation of an image sensor and that of a shutter. After this preliminary aperture adjustment, the stop member is again controlled according to a light quantity measured by the image sensor to bring it to an apposite aperture value. The aperture control is thus accomplished in two steps.
However, in case that the video camera arranged according to the above-cited prior art arrangement is to be applied to an image sensing apparatus of the kind permitting a still picture taking operation and use of an interchangeable lens in combination with an optical view finder, there arises the following problems. It is preferable for the apparatus of this kind to have a bright view finder for the purpose of determining a composition of the still picture to be taken befor an actual picture taking operation. Whereas, it is hardly possible to obtain such a bright view finder in accordance with the prior art arrangement cited above.